Polio

Definition

Poliomyelitis, also called polio or infantile paralysis, is a highly infectious viral disease that may attack the central nervous system and is characterized by symptoms that range from a mild nonparalytic infection to total paralysis in a matter of hours.

Description

There are three known types of polioviruses (called 1,2, and 3), each causing a different strain of the disease and all are members of the viral family of enteroviruses (viruses that infect the gastrointestinal tract). Type 1 is the cause of epidemics and many cases of paralysis, which is the most severe manifestation of the infection. The virus is usually a harmless parasite of human beings. Some statistics quote one in 200 infections as leading to paralysis while others state that one in 1,000 cases reach the central nervous system (CNS). When it does reach the CNS, inflammation and destruction of the spinal cord motor cells (anterior horn cells) occurs, which prevents them from sending out impulses to muscles. This causes the muscles to become limp or soft and they cannot contract. This is referred to as flaccid paralysis and is the type found in polio. The extent of the paralysis depends on where the virus strikes and the number of cells that it destroys. Usually, some of the limb muscles are paralyzed; the abdominal muscles or muscles of the back may be paralyzed, affecting posture. The neck muscles may become too weak for the head to be lifted. Paralysis of the face muscles may cause the mouth to twist or the eyelids to droop. Life may be threatened if paralysis of the throat or of the breathing muscles occurs.

Man is the only natural host for polioviruses and it most commonly infects younger children, although older children and adults can be infected. Crowded living conditions and poor hygiene encourage the spread of poliovirus. Risk factors for this paralytic illness include older age, pregnancy, abnormalities of the immune system, recent tonsillectomy, and a recent episode of excessively strenuous exercise concurrent with the onset of the CNS phase.

Causes and symptoms

Poliovirus can be spread by direct exposure to an infected individual, and more rarely, by eating foods contaminated with waste products from the intestines (feces) and/or droplets of moisture (saliva) from an infected person. Thus, the major route of transmission is fecal-oral, which occurs primarily with poor sanitary conditions. The virus is believed to enter the body through the mouth with primary multiplication occurring in the lymphoid tissues in the throat, where it can persist for about one week. During this time, it is absorbed into the blood and lymphatics from the gastrointestinal tract where it can reside and multiply, sometimes for as long as 17 weeks. Once absorbed, it is widely distributed throughout the body until it ultimately reaches the CNS (the brain and spinal cord). The infection is passed on to others when poor handwashing allows the virus to remain on the hands after eating or using the bathroom. Transmission remains possible while the virus is being excreted and it can be transmitted for as long as the virus remains in the throat or feces. The incubation period ranges from three to 21 days, but cases are most infectious from seven to 10 days before and after the onset of symptoms.

There are two basic patterns to the virus: the minor illness (abortive type) and the major illness (which may be paralytic or nonparalytic). The minor illness accounts for 80-90% of clinical infections and is found mostly in young children. It is mild and does not involve the CNS. Symptoms include a slight fever, fatigue, headache, sore throat, and vomiting, which generally develop three to five days after exposure. Recovery from the minor illness occurs within 24-72 hours. Symptoms of the major illness usually appear without a previous minor illness and generally affect older children and adults.

About 10% of people infected with poliovirus develop severe headache and pain and stiffness of the neck and back. This is due to an inflammation of the meninges (tissues which cover the spinal cord and brain). This syndrome is called "aseptic meningitis." The term "aseptic" is used to differentiate this type of meningitis from those caused by bacteria. The patient usually recovers completely from this illness within several days.

About 1% of people infected with poliovirus develop the most severe form. Some of these patients may have two to three symptom-free days between the minor illness and the major illness but the symptoms often appear without any previous minor illness. Symptoms again include headache and back and neck pain. The major symptoms, however, are due to invasion of the motor nerves, which are responsible for movement of the muscles. This viral invasion causes inflammation, and then destruction of these nerves. The muscles, therefore, no longer receive any messages from the brain or spinal cord. The muscles become weak, floppy, and then totally paralyzed. All muscle tone is lost in the affected limb and the muscle becomes soft (flaccid). Within a few days, the muscle will begin to decrease in size (atrophy). The affected muscles may be on both sides of the body (symmetric paralysis), but are often on unbalanced parts of the body (asymmetric paralysis). Sensation or the ability to feel is not affected in these paralyzed limbs.

DR. JONAS E. SALK (1914–1995)

Jonas Salk was born in New York, New York, on October 28, 1914. He received his medical degree from New York University in 1939. In 1942, Salk began working for a former teacher, Thomas Francis, Jr., to produce influenza vaccines, a project that continued until 1949. That year, as a research professor, Salk began a three-year project sponsored by the National Foundation for Infantile Paralysis, also known as the March of Dimes. Caused by the poliomyelitis virus, polio was also known as infantile paralysis. Periodic outbreaks of the disease, which attacks the nervous system, caused death or a lifetime of paralysis, especially in children. It was a difficult disease to study because sufficient viruses could not be obtained. Unlike bacteria, which can be grown in cultures, viruses need living tissue on which to grow. Once a method for preparing viruses was discovered and improved, sufficient viruses became available for research.

Salk first set out to confirm that there were three virus types responsible for polio and then began to experiment with ways to kill the virus and yet retain its ability to produce an immune response. By 1952, he had produced a dead virus vaccine that worked against the three virus types. He began testing. First the vaccine was tested on monkeys, then on children who had recovered from the disease, and finally on Salk's own family and children, none of whom had ever had the disease. Following large-scale trials in 1954, the vaccine was finally released for public use in 1955. The Salk vaccine was not the first vaccine against polio, but it was the first to be found safe and effective. By 1961, there was a 96 percent reduction in polio cases in the United States.

When poliovirus invades the brainstem (the stalk of brain which connects the two cerebral hemispheres with the spinal cord, called bulbar polio), a person may begin to have trouble breathing and swallowing. If the brainstem is severely affected, the brain's control of such vital functions as heart rate and blood pressure may be disturbed. This can lead to death.

The maximum state of paralysis is usually reached within just a few days. The remaining, unaffected nerves then begin the process of attempting to grow branches which can compensate for the destroyed nerves. Fortunately, the nerve cells are not always completely destroyed. By the end of a month, the nerve impulses start to return to the apparently paralyzed muscle and by the end of six months, recovery is almost complete. If the nerve cells are completely destroyed, however, paralysis is permanent.

Diagnosis

Fever and asymmetric flaccid paralysis without sensory loss in a child or young adult almost always indicate poliomyelitis. Using a long, thin needle inserted into the lower back to withdraw spinal fluid (lumbar puncture) will reveal increased white blood cells and no bacteria (aseptic meningitis). Nonparalytic poliomyelitis cannot be distinguished clinically from aseptic meningitis due to other agents. Virus isolated from a throat swab and/or feces or blood tests demonstrating the rise in a specific antibody is required to confirm the diagnosis.

Treatment

There is no specific treatment for polio except symptomatic. Therapy is designed to make the patient more comfortable (pain medications and hot packs to soothe the muscles), and intervention if the muscles responsible for breathing fail (for instance, a ventilator to take over the work of breathing). During active infection, rest on a firm bed is indicated. Physical therapy is the most important part of management of paralytic polio during recovery.

Prognosis

When poliovirus causes only the minor illness or simple aseptic meningitis, the patient can be expected to recover completely. When the patientis diagnosed with the major illness, about 50% will recover completely. About 25% of such patients will have slight disability, and about 25% will have permanent and serious disability. Approximately 1% of all patients with major illness die. The greatest return of muscle function occurs in the first six months, but improvements may continue for two years.

A recently described phenomenon called postpolio syndrome may begin many years after the initial illness. This syndrome is characterized by a very slow, gradual decrease in muscle strength.

Prevention

There are two types of polio immunizations available in the United States. Both of these vaccines take advantage of the fact that infection with polio leads to an immune reaction, which will give the person permanent, lifelong immunity from re-infection with the form of poliovirus for which the person was vaccinated.

The Sabin vaccine (also called the oral polio vaccine or OPV) is given to infants by mouth at the same intervals as the DPT (three doses). It contains the live, but weakened, poliovirus, which make the recipient immune to future infections with poliovirus. Because OPV uses live virus, it has the potential to cause infection in individuals with weak immune defenses (both in the person who receives the vaccine and in close contacts). This is a rare complication, however, occurring in only one in 6.8 million doses administered and one in every 6.4 million doses from having close contact with someone who received the vaccine.

The Salk vaccine (also called the killed polio vaccine or inactivated polio vaccine) consists of a series of three shots that are given just under the skin. This immunization contains no live virus, just the components of the virus that provoke the recipient's immune system to react as if the recipient were actually infected with the poliovirus. The recipient thus becomes immune to infection with the poliovirus in the future.

In the 13 years following the launching of the Global Polio Eradication Initiative, the number of cases has fallen 99% from an estimated 350,000 cases to less than 3,500 cases worldwide in 2000. At the end of 2000, the number of polio-infected countries was approximately 20, down from 125. The goal of the World Health Organization (WHO) is to have polio eliminated from the planet by the year 2005. The virus has still been identified in Africa and parts of Asia, so travelers to those areas may want to check with their physicians concerning booster vaccinations.

Resources

BOOKS

Braunwald MD, E., A. Fauci MD, D. Kasper MD, S. Hauser MD,D. Longo MD, and J. Jameson MD. Harrison's Principles of Internal Medicine. New York: McGraw-Hill, 2001.

Cecil, R., and L. Goldman. Cecil Textbook of Medicine. Philadelphia: W.B. Saunders, 1999.

PERIODICALS

Centers for Disease Control and Prevention. "Poliomyelitis prevention in the United States: Updated recommendations of the AdvisoryCommittee on Immunization Practices (ACIP)." MMWR 2000. 〈http://www.cdc.gov/〉.

OTHER

World Health Organization. "Global Polio EradicationProgress 2000." 〈http://www.polioeradication.org/〉.

KEY TERMS

Aseptic— Sterile; containing no microorganisms, especially no bacteria.

Asymmetric— Not occurring evenly on both sides of the body.

Atrophy— Shrinking; growing smaller in size.

Brainstem— The stalk of the brain which connects the two cerebral hemispheres with the spinal cord.

DPT— Diphtheria, Pertussis and Tetanus injections.

Epidemic— Refers to a situation in which a particular disease rapidly spreads among many people in the same geographical region over a small time period.

Flaccid— Weak, soft, floppy.

Gastrointestinal— Pertaining to the stomach and intestines.

Lymph/lymphatic— One of the three body fluids that is transparent and a slightly yellow liquid that is collected from the capillary walls into the tissues and circulates back to the blood supply.

Paralysis— The inability to voluntarily move.

Symmetric— Occurring on both sides of the body, in a mirror-image fashion.

Polio

What Is Polio?

How Common Is Polio?

Is Polio Contagious?

What Are the Signs and Symptoms?

How Do Doctors Make the Diagnosis?

What Is the Treatment for Polio?

What to Expect

How Can Polio Be Prevented?

Resources

Poliomyelitis (po-lee-o-my-uh-LYE-tis) is a condition caused by the polio virus that involves damage of nerve cells. It may lead to weakness and deterioration of the muscles and sometimes paralysis.

KEYWORDS

for searching the Internet and other reference sources

Albert Sabin

Inactivated poliovirus vaccine (IPV)

Jonas Salk

Oral polio vaccine (OPV)

Paralysis

Postpolio syndrome

Vaccine-associated paralytic polio (VAPP)

What Is Polio?

Poliovirus, part of the enterovirus* group, makes its home in the gastrointestinal* tract, but when the viral infection spreads it can destroy nerve cells known as motor neurons, which make muscles work. The damaged motor neurons cannot rebuild themselves, and as a result the body’s muscles no longer function correctly.

*enterovirus

(en-tuh-ro-VY-rus) is a group of viruses that can infect the human gastrointestinal tract and spread through the body causing a number of symptoms.

*gastrointestinal

(gas-tro-in-TEStih-nuhl) means having to do with the organs of the digestive system, the system that processes food. It includes the mouth, esophagus, stomach, intestines, colon, and rectum and other organs involved in digestion, including the liver and pancreas.

Poliovirus infections are broken down into four types: asymptomatic (a-simp-toh-MA-tik), abortive, nonparalytic (non-pair-uh-LIH-tik), and paralytic (pair-uh-LIH-tik). Most cases of polio cause no symptoms (asymptomatic) or only minor symptoms (abortive), such as sore throat, vomiting, or other symptoms resembling those of the flu. Nonparalytic polio has more severe symptoms, including stiff neck due to meningitis and muscle stiffness in the back and legs. Paralytic polio, the rarest but most severe form of the disease, attacks the central nervous system (the part of the nervous sysem that includes the brain and spinal cord) and can cause muscle weakness, spasms, and paralysis.

Types of paralytic polio include spinal, bulbar (BUL-bar), and bulbospinal (bul-boh-SPY-nul). The spinal type is most common, affecting the muscles of the legs, trunk, and neck. The bulbar form involves nerves of the brain stem* and can cause problems with breathing, talking, and swallowing. Bulbospinal polio is a combination of the first two types.

*brain stem

is the part of the brain that carries messages back and forth between the higher areas of the brain and the spinal cord.

How Common Is Polio?

Polio essentially has been wiped out in the United States and many other developed countries since the introduction of a polio vaccine in 1955. Before that, polio occurred in epidemic* form, with more than 21,000 paralytic cases (mostly children) in the United States in 1952 alone. The last cases of naturally occurring polio infection (known as “wild polio”) acquired in the United States were reported in 1979. In the following two decades, only 152 cases of polio were reported, most of them vaccine-associated paralytic polio (VAPP), a rare complication that strikes 1 in 2 million to 3 million people who receive the oral (by mouth) polio vaccine (OPV). The last case of VAPP was recorded in 1999, and children now receive a vaccine containing an inactivated form of the virus that cannot cause polio. Although wild polio has not been found in the United States for more than two decades, it is still present in parts of Africa and Asia.

*epidemic

(eh-pih-DEH-mik) is an outbreak of disease, especially infectious disease, in which the number of cases suddenly becomes far greater than usual. Usually epidemics are outbreaks of diseases in specific regions, whereas worldwide epidemics are called pandemics.

Is Polio Contagious?

Poliovirus is extremely contagious and can pass easily from person to person. The virus typically is found in feces* and can be transmitted when people come into contact with infected matter from bowel movements and unknowingly touch the mouth or nose without washing their hands first. The virus can live in feces for weeks, making the spread of infection difficult to control. It also can spread through contact with tiny drops of fluid from a sick person’s mouth or nose or by drinking contaminated water. After entering the mouth or nose, the virus multiplies

*feces

(FEE-seez) is the excreted waste from the gastrointestinal tract.

Ending Polio: A Timeline

1955: Jonas Salk’s vaccine containing dead, or inactive, poliovirus

(IPV) is licensed, and mass numbers of school children are vaccinated, leading to an enormous decrease in the number of polio cases over the next few years and a 60 to 70 percent prevention rate.

1963: Albert Sabin’s oral polio vaccine (OPV), containing a live but weakened virus, becomes the new recommended vaccination in the United States. It offers lifelong protection, can be swallowed, and is easy to administer; in very rare cases, however, it actually causes paralytic polio.

1979: The last cases of wild polio are reported in the United States.

2000: IPV becomes the exclusive polio vaccine used in the United States. Experts believe that because polio has virtually disappeared in the United States, the benefits of using OPV are no longer worth the very small risk of contracting the disease from OPV.

in the throat or gastrointestinal tract and eventually can invade the bloodstream. The infection is most contagious 7 to 10 days before symptoms begin and for the same period after they appear. The virus spreads more readily in areas with poor sanitation.

What Are the Signs and Symptoms?

People with abortive poliomyelitis can experience:

• fever
• headaches
• sore throat
• nausea (NAW-zee-uh) or vomiting

Nonparalytic poliomyelitis symptoms include:

• fever
• headache
• stiffness or pain in the neck, back, or legs
• muscle stiffness or spasms
• nausea and vomiting
• extreme tiredness

Paralytic poliomyelitis is marked by:

• fever
• stiffness or severe pain in the neck, back, or legs
• muscle spasms rapidly increasing muscle weakness leading to paralysis
• difficulty in urinating
• constipation
• difficulty in breathing, talking, and swallowing

How Do Doctors Make the Diagnosis?

Polio has been nearly wiped out worldwide. Because polio is no longer found in the United States, a doctor may ask about any recent travel to countries where the disease still occurs. A doctor may suspect polio in an ill patient with paralysis, particularly if the person has not been immunized against polio. During a physical examination, a doctor looks for evidence of muscle paralysis. Samples of blood, bowel movements, fluid from the throat, or cerebrospinal fluid* may be taken and tested for the virus.

*cerebrospinal

(seh-ree-bro-SPY-nuhl) fluid is the fluid that surrounds the brain and spinal cord.

What Is the Treatment for Polio?

There is no cure for polio. Easing a patient’s symptoms is the best treatment for the disease. Controlling pain and muscle spasms and watching for progression of muscle weakness so supportive care can be given are the main parts of treatment. Abortive cases and many nonparalytic cases of polio usually are helped by rest, fluids, and pain medication. Moist heat on muscles can ease stiffness. Antibiotics may be prescribed to treat bacterial infections that can occur in patients with polio, such as urinary tract infections*.

*urinary tract infections ,

or UTIs, are infections that occur in any part of the urinary tract. The urinary tract is made up of the urethra, bladder, ureters, and kidneys.

Patients with severe cases of polio, particularly the paralytic form, often require hospitalization. In the 1940s and 1950s, patients were placed inside metal tanks called “iron lungs” that assisted their breathing. Although medical technology has progressed since then, many people who have polio still need machines called ventilators* to assist breathing as they recover, as well as additional supportive care. Patients with paralytic polio may need physical therapy, crutches, leg braces, or surgery to help them regain their strength and movement.

*ventilator

(VEN-tuh-lay-ter) is a machine used to support or control a person’s breathing.

What to Expect

If the disease does not damage the spinal cord and brain, patients typically make a full recovery. Symptoms in cases of abortive polio generally last less than a week, whereas in nonparalytic cases symptoms can last 1 to 2 weeks. If the polio infection causes paralysis, it can take months for muscles to begin to regain their strength and mobility. Paralysis that lingers after 12 months usually is considered permanent. Complications include:

• permanent paralysis, usually in the legs but sometimes in other muscles as well
• breathing problems due to muscle paralysis or damage to areas of the brain that control breathing
• pneumonia* due to swallowing difficulties

*pneumonia

(nu-MO-nyah) is inflammation of the lung.

• fluid in the lungs
• urinary tract infections
• kidney stones*

*kidney stones

are hard structures that form in the urinary tract. These structures are composed of crystallized chemicals that have separated from the urine. They can obstruct the flow of urine and cause tissue damage and pain as the body attempts to pass the stones through the urinary tract and out of the body.

• high blood pressure
• postpolio syndrome, which affects 25 to 50 percent of people previously infected and develops 15 to 40 years after the initial infection, causing symptoms of muscle pain, new or increased weakness, and paralysis

How Can Polio Be Prevented?

The polio vaccine is the best way to prevent the disease; its use has eliminated polio from the Western Hemisphere. Jonas Salk developed the first vaccine in 1955. It is known as inactivated poliovirus vaccine (IPV), because the poliovirus used to make the vaccine was “killed,” or inactivated. Several years later, Albert Sabin developed an oral polio vaccine, which was given in the form of drops that could be swallowed. These drops contained a live, but weakened, virus.

OPV was very successful in helping rid the United States of polio. Its advantage over IPV was that once children had been immunized, they could pass the weakened virus to others who had not received the vaccine in the same way that the infectious poliovirus spread between people. This contact with the virus gave unvaccinated children immunity as if they had been vaccinated. In rare cases, however, because it contained a live virus OPV actually caused paralytic polio in the children who received the vaccine or in people who had close contact with them and had not been immunized. This is known as vaccine-associated paralytic polio. People with weakened immune systems were most at risk for VAPP.

IPV is now the only polio vaccine used in the United States, and it does not cause VAPP. Children might have a sore spot where they receive the shot, but there are rarely any side effects from the vaccine. Children receive IPV routinely as part of the childhood immunization schedule. Most adults who were vaccinated as children do not need to receive the vaccine again. People traveling to places where polio is still found (such as Africa and Asia), lab workers who handle poliovirus, and medical professionals who care for patients with polio may need to be vaccinated again. If polio is wiped out worldwide, immunization against polio may not be needed in the future.

See also

Meningitis

Vaccination (Immunization)

Resources

Organization

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. Through the website of the National Immunization Program, the CDC provides information about polio and immunization schedules and vaccines.

Telephone 800-311-3435 http://www.cdc.gov/nip/

Websites

KidsHealth.org. KidsHealth is a website created by the medical experts of the Nemours Foundation and is devoted to issues of children’s health. It contains articles on a variety of health topics, including polio.

http://www.KidsHealth.org

The Public Broadcasting System traces the history of polio in the United States through its companion website to the video A Paralyzing Fear: The Story of Polio in America.

http://www.pbs.org/storyofpolio/polio/index.html

The World Health Organization’s Global Polio Eradication Initiative website offers facts, news, and immunization information about the disease.

http://www.polioeradication.org

Polio

Definition

Poliomyelitis, also called polio or infantile paralysis, is a highly infectious viral disease that may attack the central nervous system and is characterized by symptoms that range from a mild nonparalytic infection to total paralysis in a matter of hours.

Description

There are three known types of polioviruses (called 1, 2, and 3), each causing a different strain of the disease and all being members of the viral family of enteroviruses (viruses that infect the gastrointestinal tract). Type 1 is the cause of epidemics, and many cases of paralysis, which is the most severe manifestation of the infection. The virus is usually a harmless parasite of human beings. Some statistics quote one in 200 infections as leading to paralysis, while others state that one in 1,000 cases reach the central nervous system (CNS). When it does reach the CNS, inflammation and destruction of the spinal cord motor cells (anterior horn cells) occurs, which prevents them from sending out impulses to muscles. This causes the muscles to become limp or soft, and they cannot contract, a condition called flaccid paralysis and is the type found in polio. The extent of the paralysis depends on where the virus strikes and the number of cells that it destroys. Usually, some of the limb muscles are paralyzed; the abdominal muscles or muscles of the back may be paralyzed, affecting posture. The neck muscles may become too weak for the head to be lifted. Paralysis of the face muscles may cause the mouth to twist or the eyelids to droop. Life may be threatened if paralysis of the throat or of the breathing muscles occurs.

Humans are the only natural host for polioviruses, and it most commonly infects younger children, although older children and adults can be infected. Crowded living conditions and poor hygiene encourage the spread of poliovirus. Risk factors for this paralytic illness include older age, pregnancy, abnormalities of the immune system, and a recent episode of excessively strenuous exercise concurrent with the onset of the CNS phase. As of 2004, the last naturally occurring polio case in the United States was diagnosed in 1979.

Causes and symptoms

Poliovirus can be spread by direct exposure to an infected individual, and more rarely, by eating foods contaminated with waste products from the intestines (feces) and/or droplets of moisture (saliva) from an infected person. Thus, the major route of transmission is fecal-oral, which occurs primarily with poor sanitary conditions. The virus is believed to enter the body through the mouth with primary multiplication occurring in the lymphoid tissues in the throat, where it can persist for about one week. During this time, it is absorbed into the blood and lymphatics from the gastrointestinal tract where it can reside and multiply, sometimes for as long as 17 weeks. Once absorbed, it is widely distributed throughout the body until it ultimately reaches the CNS (the brain and spinal cord). The infection is passed on to others when poor hand washing allows the virus to remain on the hands after eating or using the bathroom. Transmission remains possible while the virus is being excreted and it can be transmitted for as long as the virus remains in the throat or feces. The incubation period ranges from three to 21 days, but cases are most infectious from seven to ten days before and after the onset of symptoms.

There are two basic patterns to the virus: the minor illness (abortive type) and the major illness (which may be paralytic or nonparalytic). The minor illness accounts for 80 to 90 percent of clinical infections and is found mostly in young children. It is mild and does not involve the CNS. Symptoms include a slight fever , fatigue, headache , sore throat , and vomiting , which generally develop three to five days after exposure. Recovery from the minor illness occurs within 24 to 72 hours. Symptoms of the major illness usually appear without a previous minor illness and generally affect older children and adults.

About 10 percent of people infected with poliovirus develop severe headache and pain and stiffness of the neck and back. This is due to an inflammation of the meninges (tissues which cover the spinal cord and brain). This syndrome is called aseptic meningitis . The term aseptic is used to differentiate this type of meningitis from those caused by bacteria. The patient usually recovers completely from this illness within several days.

About 1 percent of people infected with poliovirus develop the most severe form. Some of these patients may have two to three symptom-free days between the minor illness and the major illness, but the symptoms often appear without any previous minor illness. Symptoms again include headache and back and neck pain. The major symptoms, however, are due to invasion of the motor nerves, which are responsible for movement of the muscles. This viral invasion causes inflammation and then destruction of these nerves. The muscles, therefore, no longer receive any messages from the brain or spinal cord. The muscles become weak, floppy, and then totally paralyzed. All muscle tone is lost in the affected limb and the muscle becomes soft (flaccid). Within a few days, the muscle begins to decrease in size (atrophy). The affected muscles may be on both sides of the body (symmetric paralysis) but are often on unbalanced parts of the body (asymmetric paralysis). Sensation or the ability to feel is not affected in these paralyzed limbs.

When poliovirus invades the brainstem (the stalk of brain which connects the two cerebral hemispheres with the spinal cord, called bulbar polio), a person may begin to have trouble breathing and swallowing. If the brainstem is severely affected, the brain's control of such vital functions as heart rate and blood pressure may be disturbed, a condition that can lead to death.

The maximum state of paralysis is usually reached within just a few days. The remaining, unaffected nerves then begin the process of attempting to grow branches, which can compensate for the destroyed nerves. Fortunately, the nerve cells are not always completely destroyed. By the end of a month, the nerve impulses start to return to the apparently paralyzed muscle and by the end of six months, recovery is almost complete. If the nerve cells are completely destroyed; however, paralysis is permanent.

Diagnosis

Fever and asymmetric flaccid paralysis without sensory loss in a child or young adult almost always indicate poliomyelitis. Using a long, thin needle inserted into the lower back to withdraw spinal fluid (lumbar puncture) will reveal increased white blood cells and no bacteria (aseptic meningitis). Nonparalytic poliomyelitis cannot be distinguished clinically from aseptic meningitis due to other agents. Virus isolated from a throat swab and/or feces or blood tests demonstrating the rise in a specific antibody is required to confirm the diagnosis.

Treatment

There is no specific treatment for polio except symptomatic. Therapy is designed to make the patient more comfortable (pain medications and hot packs to soothe the muscles), and intervention if the muscles responsible for breathing fail (for instance, a ventilator to take over the work of breathing). During active infection, rest on a firm bed is indicated. Physical therapy is the most important part of management of paralytic polio during recovery.

Prognosis

When poliovirus causes only the minor illness or simple aseptic meningitis, the patient can be expected to recover completely. Among patients with the major illness, about 50 percent recover completely. About 25 percent of such patients have slight disability, and about 25 percent have permanent and serious disability. Approximately 1 percent of all patients with major illness die. The greatest return of muscle function occurs in the first six months, but improvements may continue for two years.

Post-polio syndrome (PPS) is a condition that can strike polio survivors anywhere from 10 to 40 years after their recovery from polio. It is caused by the death of individual nerve terminals in the motor units that remain after the initial polio attack. Symptoms include fatigue, slowly progressive muscle weakness, muscle and joint pain, and muscular atrophy. The severity of PPS depends upon how seriously the survivors were affected by the first polio attack.

Prevention

There are two types of polio immunizations available in the United States, but since the year 2000, one is rarely used. A vaccine takes advantage of the fact that infection with polio leads to an immune reaction, which will give the person permanent, lifelong immunity from reinfection with the form of poliovirus for which the person was vaccinated.

The Salk vaccine (also called the killed polio vaccine or inactivated polio vaccine, IPV) consists of a series of three shots that are given just under the skin to children at the ages of two months, four months, and any time between six and 18 months. A fourth injection is given between the ages of four to six years as a booster. This immunization contains no live virus, just the components of the virus that provoke the recipient's immune system to react as if the recipient were actually infected with the poliovirus. The recipient thus becomes immune to infection with the poliovirus.

KEY TERMS

Aseptic —Sterile; containing no microorganisms, especially no bacteria.

Asymmetric —Not occurring equally on both sides of the body.

Atrophy —The progressive wasting and loss of function of any part of the body.

Brainstem —The stalk of the brain which connects the two cerebral hemispheres with the spinal cord. It is involved in controlling vital functions, movement, sensation, and nerves supplying the head and neck.

Epidemic —Refers to a situation in which a particular disease rapidly spreads among many people in the same geographical region in a relatively short period of time.

Flaccid —Flabby, limp, weak, or floppy.

Gastrointestinal —Pertaining to the digestive organs and structures, including the stomach and intestines.

Lymph —Clear, slightly yellow fluid carried by a network of thin tubes to every part of the body. Cells that fight infection are carried in the lymph.

Paralysis —Loss of the ability to move one or more parts of the body voluntarily due to muscle or nerve damage.

Symmetric —Occurring on both sides of the body, in a mirror-image fashion.

Since the year 2000, the Sabin vaccine (also called the oral polio vaccine or OPV) has been discontinued in the United States, although it is still being used in other countries. It contains the live, but weakened, poliovirus and because OPV uses the live virus, it has the potential to cause infection in individuals with weak immune defenses (both in the person who receives the vaccine and in close contacts). Approximately nine cases a year of vaccine related polio was associated with OPV in the United States. Although this is a rare complication, occurring in only one in 6.8 million doses administered and one in every 6.4 million doses from having close contact with someone who received the vaccine, the risk of having polio from OPV was greater than it was of naturally acquiring it.

Following the launching of the Global Polio Eradication Initiative, the number of cases fell 99 percent from an estimated 350,000 cases to less than 3,500 cases worldwide in 2000. At the end of 2000, the number of polio-infected countries was approximately 20, down from 125. The goal of the World Health Organization (WHO) is to have polio eliminated from the planet by the year 2005. The virus has still been identified in Africa and parts of Asia, so travelers to those areas may want to check with their physicians concerning booster vaccinations.

Resources

BOOKS

Oshinsky, David. Polio: An American Story. Oxford, UK: Oxford University Press, 2004.

PERIODICALS

Alexander, L. N., et al. "Vaccine Policy Changes and Epidemiology of Poliomyelitis in the United States" Journal of the American Medical Association 292 (2004): 1696–1701.

ORGANIZATION

International Polio Network. 4207 Lindell Blvd., Suite 110, St. Louis, MO 63108–2915. Web site: <www.postpolio.org>.

March of Dimes Birth Defects Foundation. National Office, 1275 Mamaroneck Avenue, White Plains, NY 10605. Web site: <www.modimes.org/>.

WEB SITES

World Health Organization. Global Polio Eradication Progress 2004. Available online at <www.polioeradication.org/>.

Linda K. Bennington, MSN,CNS

Polio

Poliomyelitis, or infantile paralysis, is a virus disease affecting the central nervous system. The infection passes from person to person by the fecal-oral route. Throughout most of human history the polio virus was ubiquitous and infected almost all children as soon as they were weaned from breast milk to a mixed diet, but infection caused symptoms in only a small minority. Infants exposed to the polio virus when they were first weaned retained some residual maternal immunity, or else the virus was less virulent before the early twentieth century when the disease began occurring in epidemics of paralytic poliomyelitis. For either or both of these reasons, the infection usually passed unnoticed since it caused neither symptoms nor signs.

Early History

Poliomyelitis occurs when the virus invades the nervous system and attacks nerves that activate muscle movement, but in many cases infection with the polio virus causes no signs or symptoms at all. The symptoms include fever, headache, and muscle pains, rapidly followed by the onset of localized muscle paralysis, which is permanent. Depending on which nerves are attacked–that is, which muscles are paralyzed– the outcome varies from mild weakness of part of an arm or leg to death if nerves in the brain stem that control muscles required for breathing and swallowing are paralyzed. Until about the 1920s polio was a disease of infants and young children, but older children, adolescents, and adults occasionally got it too. When a limb was paralyzed in childhood, the muscles wasted away and the limb did not continue to develop at the same rate as that on the unaffected side, leading to a shriveled arm or leg or some worse deformity, depending upon the severity of the disease.

We know that poliomyelitis has existed for thousands of years. A stone carving from Egypt, dated about 1500 b.c.e., shows a youth with the deformed shrunken leg that is characteristic of polio and has virtually no other possible cause. The old name for the disease, infantile paralysis, recalls the time when it was primarily a disease of infants and very young children and its outcome was paralysis of the affected muscles. Both the little crippled boy who could not follow the Pied Piper of Hamelin and Tiny Tim in Charles Dickens' classic A Christmas Carol, were probably victims of infantile paralysis. Because of its fecal-oral transmission route and because of ecological factors such as the prevalence of flies to carry fecal contamination to food in summer, poliomyelitis was always predominantly a summertime disease.

Polio Epidemics

When standards of domestic hygiene and environmental sanitation began to improve in the rich nations of Europe and North America after the sanitary reforms of the late nineteenth and early twentieth centuries, infants often escaped infection and the disease began to have a greater impact on older children, adolescents, and young adults, and began to occur in epidemics. Repeated epidemics affecting significant numbers of children, adolescents, and young adults became commonplace in North America, Europe, and Australia early in the twentieth century.

These epidemics had dramatic effects on family life and society at a time when infant mortality and family size were declining. The life and health of every child seemed more precious to most people than perhaps it had in the days when it was an accepted fact of life that a great many newborn infants did not survive. And it was almost as bad for parents to see their children struck down by a disease that left them crippled as to see them die. Parents sometimes took extraordinary precautions to protect their children. Polio was known to be due to an infectious pathogen but until the 1950s it was not known how this pathogen was transmitted. In the large epidemics of the 1930s and 1940s, schools, cinemas, public swimming pools, and sports arenas were closed, perhaps reinforcing a mood of mass anxiety bordering on hysteria that the size and true impact of these epidemics did not justify. The epidemics were in fact numerically small in comparison to the great epidemics of cholera, typhus, and smallpox of the nineteenth century.

The Medical Response

The medical response was more rational. Special hospital facilities were developed to deal with the care of children and young adults with paralyzed respiratory muscles. Modern intensive-care nursing and specialized intensive care units evolved from the early treatment of severe epidemic poliomyelitis, which was still often called infantile paralysis. Cecil Drinker (1887-1956), an American physiologist, invented a respirator commonly known as an iron lung, in which children with paralyzed respiratory muscles were nursed, often for many months or even years, and their breathing was maintained by means of a pistonlike device that kept air pressure below atmospheric level, expanding the chest as air was sucked into the lungs. The machines, the intensive nursing care that was required with them, the prolonged aftercare with skilled physiotherapy, and appliances to assist paralyzed people to get about, were costly. When Franklin Delano Roosevelt was struck down with severe polio in 1921, the disease and its expensive treatment and aftercare acquired a high public profile. The charitable foundation March of Dimes, founded in 1935, was born in a wave of massive public sympathy for the young victims of infantile paralysis. Unlike other charitable foundations of that time, the March of Dimes relied on innumerable small donations rather than a few large ones, and in this way it was able to raise enough money not only to pay for many of the expensive treatment facilities but also to invest in research.

Research focused partly on improved treatment and rehabilitation methods, but it was much more important to find a way to prevent the disease. This required discovery of the causative organism, epidemiological studies to elucidate the way polio was spread, and development of ways to prevent the spread and immunize infants and children. All these advances were among the achievements of medical science in the first half of the twentieth century. The virus responsible for the infection was discovered in 1908 by the Austrian microbiologist Karl Landsteiner (1868-1943) and the discovery was confirmed in 1910 by Simon Flexner (1863-1946) at the Rockefeller Institute in New York. These discoveries, in the early years of virology, were based on inference as much as on direct observation.

Development of a vaccine to protect against infection could not begin until ways to cultivate the virus artificially were developed. Before this happened, several therapeutic innovations emerged, sometimes with unhappy consequences. Vaccine trials in 1935, using convalescent human serum, may actually have enhanced the risk of paralytic polio and may also have transmitted other virus diseases such as hepatitis. Sister Elizabeth Kenny, an Australian nurse, advocated movement and massage of affected limbs, in contrast to the then-orthodox procedures of immobilization for prolonged periods. Her ideas were theoretically sound but in practice sometimes did more harm than good.

The first important breakthrough on the way to developing polio vaccines was the work by John Enders (1897-1985) and colleagues, who successfully grew the polio virus in tissue cultures in 1949. Jonas Salk (1914-1995) used tissue cultures of polio virus to produce the first successful vaccine that could provide immunological protection against poliomyelitis. The Salk vaccine was tested in the early 1950s and licensed for general use in 1955. The Salk vaccine had to be given by injection and was sensitive to temperature extremes. Albert Sabin (1906-1993) developed a vaccine that used live attenuated polio virus, which could be orally administered as a drop of vaccine on the tongue (or on a sugar lump) and was better able to withstand tropical temperatures; the Sabin vaccine came into general use around 1960 and superceded the Salk vaccine, despite the small (and mostly theoretical) risk that the live virus vaccine might mutate under some circumstances into a more virulent strain that could cause paralytic poliomyelitis.

The use of polio vaccines has virtually eliminated poliomyelitis from much of the world. The disease was declared eradicated from the western hemisphere in 1994. It remains a risk in low-income countries in Africa and Asia and among small groups of people such as members of certain religious sects who for reasons connected with their faith refuse to accept vaccination against poliomyelitis and other diseases.

See also: Contagious Diseases; Vaccination.

bibliography

Paul, J. R. 1971. A History of Poliomyelitis. New Haven: Yale University Press.

Robbins, F. C. 1999. "The History of Polio Vaccine Development." In Vaccines, 3rd edition, ed. S. A. Plotkin and W. A. Orenstein. Philadelphia: Saunders.

Zuber, P. L. F. 2002. "Poliomyelitis." In Encyclopedia of Public Health, ed. L. Breslow, B. D. Goldstein, L. W. Green, et al., pp. 932-933. New York: Macmillan.

John M. Last

POLIO

DEFINITION

Polio (pronounced POH-lee-oh) is a serious disease caused by a virus called the poliovirus. The full medical name for the disease is poliomyelitis (pronounced POH-lee-oh-mi-uh-LI-tis). In its severest form, polio causes paralysis of the muscles of the legs, arms, and respiratory (breathing) system.

DESCRIPTION

The poliovirus causes most of its infections in the summer and fall. At one time, summer epidemics of polio were common and greatly feared.

The poliovirus primarily affects younger children. But it can also infect older children and adults. Poor hygiene and crowded living conditions encourage the spread of the poliovirus.

Paralysis is the most serious symptom of polio. Only about 1 percent to 2 percent of those infected with the virus are paralyzed, however. Risk factors for paralysis include older age, pregnancy, problems with the immune system, a recent tonsillectomy, and a recent episode of very strenuous exercise.

Polio: Words to Know

Brain stem:

A mass of nervous tissue that connects the main part of the brain to the spinal cord.

Epidemic:

The widespread occurrence of a disease over a large geographic area for an extended period of time.

Paralysis:

The inability to move one's muscles.

CAUSES

Poliovirus is transmitted through saliva and feces. It is passed on when people do not wash their hands after eating or using the bathroom. Once a person is infected with the virus, it can remain in the mouth and throat for about three weeks. It then travels to the intestine. It can remain in the intestine for up to eight weeks.

Inside the intestine, the virus multiplies rapidly. It may invade the lymphatic (pronounced lim-FAT-ic) system. The lymphatic system consists of organs and tissues that help protect a person against disease. The virus eventually enters the bloodstream. It can then pass to the central nervous system (the brain and spinal cord). The virus can also pass directly into nerves. It can then travel along a nerve to the brain.

SYMPTOMS

About 90 percent of those infected with poliovirus have mild or no symptoms. These symptoms include a low fever, fatigue, headache, sore throat, and nausea and vomiting. These symptoms usually last two or three days. People with these symptoms are still infectious and can pass the disease on to other people.

Another 10 percent of those infected with the virus experience more serious symptoms, including severe headache and pain and stiffness of the neck and back. The stiffness is caused when the tissues around the spinal cord and brain become inflamed. These symptoms usually disappear after several days. The patient usually experiences complete recovery.

THE IRON LUNG

People with polio often lose the ability to move their legs and/or arms. This disability is a terrible disaster. But it does not necessarily cause death. If polio also causes loss of control over the respiratory muscles, however, death can and often does occur. For polio patients, then, a device to help them breathe is an absolute necessity.

In 1982, the American physiologist Philip Drinker (1893–1977) invented the most famous of all devices for helping polio patients to breathe. The device was called the Drinker tank respirator. It is more commonly known as an iron lung.

The iron lung is an airtight cylindrical steel drum. It encloses the entire body with only the patient's head exposed. Pumps connected to the device lower and raise air pressure within the drum. As the drum contracts and expands, it forces the patient's chest to contract and expand also. The iron lung forces the patient's body to continue breathing.

Many polio patients were kept alive by the iron lung. They had to spend many years enclosed in the lung, with only short periods outside it. With the development of the Salk and Sabin vaccines, polio has nearly become extinct. As a result, the iron lung no longer finds much use in today's hospitals.

About 1 percent of people infected with the poliovirus develop the most serious symptoms of the disease. At first, they experience only mild symptoms. After a few days, however, the symptoms become much worse. They include severe headache and neck and back pain.

The worst effects of polio are caused when the virus invades motor nerves. Motor nerves are nerves that control the movement of muscles. The virus can destroy these nerves. As the nerves die, muscles lose their ability to move. They first become floppy and weak. Eventually they become paralyzed and lose the ability to move at all. After a few days, the muscles actually begin to decrease in size. The person does not lose the sense of touch in the affected areas, however.

The virus can also infect the brain stem. The brain stem is located at the base of the brain. It connects the brain to the spinal cord. A person may have trouble breathing and swallowing. In the severest cases, the heart rate and blood pressure may be disturbed. These changes can lead to the patient's death.

The maximum degree of paralysis usually occurs within a few days. After that time, some healthy nerves may try to take the place of the damaged nerves. This process lasts about six months. After that time, no further improvement is likely.

DIAGNOSIS

Polio is now a rare disease in the United States. Many doctors have never seen a case of polio. A few symptoms are quite distinctive, however. A fever and paralysis without the loss of feeling is one clue to the presence of polio.

If a doctor suspects polio, the usual follow-up test is a lumbar puncture, or "spinal tap." A lumbar puncture is a procedure in which a sample of spinal fluid is removed with a long, thin needle. The spinal fluid can be examined for an elevated level of white blood cells and the absence of bacteria. These two factors taken together are a strong indication of polio.

The spinal fluid can also be tested for the presence of polio antibodies. Antibodies are chemicals produced by the immune system to fight against specific foreign invaders, such as the poliovirus.

TREATMENT

There is no cure for polio. Patients can be treated to make them more comfortable, however. For example, medications can reduce pain. Hot packs help soothe sore muscles. Artificial ventilation (breathing machines) may be necessary if a person's respiratory system is affected. Walking aids, such as crutches and walkers, may be necessary for someone whose leg muscles are damaged by the disease.

PROGNOSIS

The prognosis for mild and moderate polio is good. Most patients recover completely within a short period of time. Of those who have the severest form of polio, about half will recover completely. A quarter will experience some disability, and another quarter will have permanent and serious disability. About 1 percent of all those who have the most serious form of polio die of the disease.

In recent years, a new medical problem known as postpolio syndrome has been diagnosed. The condition shows up thirty years or more after a person has had a mild or moderate form of the disease. Postpolio syndrome affects about 25 percent of polio patients. The major symptom of postpolio syndrome is a very slow decrease in muscle strength.

PREVENTION

Polio can now be prevented by immunizations. An immunization is an injection that protects a person against some type of infectious disease. Two kinds of polio immunizations are available in the United States. The Salk vaccine contains dead polioviruses. It is injected just under the skin. The dead viruses cause the immune system to start making antibodies against the poliovirus. If a person is infected with the poliovirus later in life, the immune system can protect the body against the disease.

The Sabin vaccine contains polioviruses that are very weak but not dead. They produce the same effect on the immune system as dead viruses. Both vaccines are highly effective in preventing polio. In fact, some public-health experts think the disease may be completely wiped out in the next decade.

FOR MORE INFORMATION

Books

Daniel, Thomas M., and Frederick C. Robbins, eds. Polio. Rochester: University of Rochester Press, 1997.

Gould, Tony. A Summer Plague: Polio and Its Survivors. New Haven, CT: Yale University Press, 1997.

Halstead, Lauro S., ed. Managing Post Polio: A Guide to Living Well with Post Polio. Arlington, VA: ABI Professional Publications, 1998.

Weaver, Lydia. Close to Home: A Story of the Polio Epidemic. New York: Puffin, 1997.

Organizations

International Polio Network. 4207 Lindell Blvd., Suite 110, St. Louis, MO 63108–2915. (314) 534–0475.

March of Dimes Birth Defects Foundation. National Office. 1275 Mamaroneck Ave., White Plains, NY 10605. http://www.modimes.org.

Polio Survivors Association. 12720 Lareina Ave., Downey, CA 90242. (310) 862–4508.

Web sites

"Ask NOAH About: Neurological Problems." NOAH: New York Online Access to Health. [Online] http://www.noah.cuny.edu/neuro/neuropg.html# POLIO AND POST-POLIO SYNDROME (accessed on October 28, 1999).

Polio.com. [Online] http://www.polio.com (accessed on October 28, 1999).

"Polio/Post-Polio Information Directory." Polio Society Home Page. http://www.polio.org (accessed on October 28, 1999).